zhishu.java

来自「java应用举例1」· Java 代码 · 共 28 行

public class ZhiShu {
    public static void main(String[] args) {
        int max = 100;                           
        try { max = Integer.parseInt(args[0]); } 
        catch (Exception e) {}   

        boolean[] number = new boolean[max+1];

        for(int i = 0; i <= max; i++) number[i] = true;

        number[0] = number[1] = false;
        
        int n = (int) Math.ceil(Math.sqrt(max));  

        for(int i = 0; i <= n; i++) {
            if (number[i])                          
                for(int j = 2*i; j <= max; j = j + i)
                    number[j] = false;               
        }

        int largest;
        for(largest = max; !number[largest]; largest--) ; 
        
        System.out.println("The largest prime less than or equal to " + max +
			   " is " + largest);
    }
}